This example shows a vertical tree diagram that categorizes mobile phones by operating system, with Android, iOS, and Others as the three main branches. The tree layout uses `d3.tree()` to position the hierarchy from top to bottom, with root nodes colored by depth using a `d3.scaleOrdinal()` color scheme. Data is defined inline as a JavaScript object and rendered as SVG circles and text labels, connected by curved paths generated with `d3.linkVertical()`. The visualization uses D3 v7 to compute the layout and bind data to SVG elements.